Dual crystal fields synergistic catalytic oxygen reduction reaction regulated via Ba doping in Sm1-xBaxMn2O5

To enhance the synergistic catalytic effect of pyramid Mn 3+ and octahedral Mn 4+ dual crystal fields in SmMn 2 O 5 and improve its oxygen reduction reaction (ORR) performance, Ba-doped Sm 1-x Ba x Mn 2 O 5 (x = 0.1–0.5) catalysts were prepared by hydrothermal method. The substitution of partial Sm 3+ in SmMn 2 O 5 by Ba 2+ leads to the increase in the ratios of Mn 4+ /Mn 3+ and surface adsorbed oxygen/lattice oxygen on the surfaces of Sm 1-x Ba x Mn 2 O 5 . The increase in surface adsorbed oxygen content indicates stronger oxygen adsorption capacity, while the increase in Mn 4+ content facilitates synergistic catalysis of the dual crystal fields. Pyramid Mn 3+ acts as the active site to catalyze ORR, while the increase in octahedral Mn 4+ content enhances the catalytic activity of Mn 3+ by reducing the binding energy between Mn 3+ and oxygen-containing intermediates, weakening the Mn 3+ -O bond, and accelerating the decomposition of hydrogen peroxide generated by Mn 3+ during the ORR process. Sm 0.6 Ba 0.4 Mn 2 O 5 exhibits excellent ORR performance owing to the suitable Mn 4+ /Mn 3+ ratio on its surface, the half-wave potential reaches 0.77 V, higher than the 0.72 V of SmMn 2 O 5 , and the diffusion-limited current density increases from 3.50 mA·cm −2 for SmMn 2 O 5 to 5.03 mA·cm −2 . Moreover, the synergistic catalytic mechanism of the dual crystal fields was well discussed.